1. Field of the Invention
The present invention relates to a device intended for the compression of multiphase fluids which, prior to being compressed and under the pressure and temperature conditions considered, consist of a mixture of notably a liquid phase and a gas phase that are not dissolved in the liquid, and this liquid may or may not be gas-saturated.
2. Description of the Prior Art
Whatever the design of the pumps used (reciprocating pumps, rotary pumps or horn effect pumps), good results are obtained when the value of the volumetric ratio of the fluid is very low or even zero, because the fluid then acts as a liquid single-phase fluid. These materials can be used when their operating conditions cause no phenomena likely to allow vaporization of a large part of the gas dissolved in the liquid, or when the value of the volumetric ratio at the pump inlet is at most 0.2. It is known from experience that, above this value, the effectiveness of these devices decreases very quickly.
In order to improve the operation of existing devices, a solution consists in separating the liquid phase from the gas phase prior to pumping, and in processing the phases separately, in distinct compression circuits respectively suited to communicate a compression value to a mainly liquid phase or to a mainly gaseous phase. Separate circuits cannot always be used and often lead to bigger, more expensive and more complex pumping systems.
This is the reason why attempts have been made to develop pumping devices suited not only to increase the total energy of the multiphase fluid, but also capable of producing a multiphase fluid whose volumetric ratio value at the outlet of the pumping device is below the value thereof prior to pumping.
The prior art describes various blade profiles allowing the obtaining of this result, notably the Assignee's French Patents 2,157,437, 2,333,139, 2,471,501 and 2,665,224, which describe precise blade profiles or a geometry selected for the section of flow of the fluid defined by two successive blades. In any case, these profiles relate to simple blades comprising a single piece, unlike the blades referred to as "blades of tandem design" which comprise at least two blades within a single group.
The performances of multiphase fluid pumping with "simple" blades can be improved.
The prior art thus describes, for example in the article "Optimization for Rotor Blades of Tandem Design for Axial Flow Compressors" published in the Journal of Engineering for Power, Vol.102, p.369, in April 1980, the use of compression devices comprising blades of tandem design.
However, the teaching of this prior art only relates to the compression of single-phase fluids, i.e. fluids that, at the inlet of the compression device, mainly consist of a single phase, either liquid or gaseous. The geometric characteristics of the blades of tandem design described in this document are particularly well-suited for the compression of a single-phase fluid whose behaviour in compression can nevertheless not be compared to the behaviour of a fluid having several phases, for example fluids with at least one liquid phase and at least one gas phase, and they are therefore not suited for pumping a multiphase fluid.
It has been discovered, which is one object of the present invention, that pumping of a multiphase fluid can be improved by using blades of tandem design or "tandem blades" whose geometric configuration is suited to compress a multiphase fluid comprising at least one liquid phase and at least one vapor or gas phase, the proportions of these two phases being likely to vary with time.
In the description hereafter, the skeleton of a blade is defined as the surface which is equidistant at any point to the lower face of the blade and the upper face of the blades.
Considering the intersection of a blade with a surface of the flowing fluid around this blade, a profile for the blade may be defined from geometrical coordinates of the line of the curvature of the blade and the way it varies with the thickness of the blade along this line.